The problem concerning the greenhouse effects of human activities has broadened in scope frbm the CO2-climate problem to the trace gas-climate problem. The climate effects of non-CO 2 trace gases are strongly governed by interactions between chemistry, radiation, and dynamics. We discuss in delfiil the natuie of the trace gas radiative heating and describe the importance of radiative-chemical interactions within the troposphere and the stratosphere. We make an assessment of the trace gas effects on troposphere-stratosphere temperature trends for the period covering the preindustrial era to the present and for the next several decades. Non-CO 2 greenhouse gases in the atmosphere are now adding to the greenhouse effect by an amount comparable to the effect of CO 2. The rate of decadal increase of the total greenhouse forcing is now 3-6 times greater than the mean rate for th where it is the climate feedback parameter and •: is the effective ocean thermal diffusivity. Th• magnitude of it, which also governs the equilibrium surface warming, is governed strongly by radiative and dynaniical processes in the atmosphere, and hence the effect of oceans on transient climate change is determined by the interactions between atmospheric and oceanic dynamical as well as radiative processes. The next crucial issue concerns accurate determination of decadal trends in radiative forcings, trace gases, planetary albedo (to determine effects of aerosols and cloud feedback), and surface-troposphere-stratosphere temperatures. The observational challenges are formidable and must be overcome for a scientifically credible interpretation of the human impacts on climate.

An international program of intercomparison of radiation models has been initiated because of the central role of radiative processes in many proposed climate change mechanisms. Models ranging from the most detailed (line-by-line) to the most-highly parameterized have been compared with each other and with selected aircraft observations. Although line-by-line-model fluxes tend to agree with each other to within one percent (if the water-vapor-continuum absorption is ignored), the lessdetailed models show a spread of 10-20 percent. The spread is even larger (30-40 percent) for the sensitivities of the models to changes in important radiation variables, such as carbon dioxide amounts and water-vapor amounts. These spreads are disturbingly large.Lacking highly accurate flux observations from within the atmosphere, it has been customary to regard line-by-line-model results as "the truth." However, uncertainties in the physics of line wings and in the proper treatment of the water-vapor continuum make it impossible for the line-by-line models to provide an absolute reference for evaluating less-detailed models. Therefore, a dedicated surface-based field measurement program is recommended in order to properly evaluate model performance; the goal would be to use sophisticated spectrometers to measure accurately spectral radiances rather than integrated fluxes.

No abstract

Results are presented from an extensive theoretical investigation aimed at evaluating the effect of molecular multiple scattering and surface albedo on photodissociation rates. Results are compared with similar calculations typical of most atmospheric photochemical models which only describe absorption in a direct solar beam. The effect of molecular multiple scattering and surface albedo on photodissociation rates, which can be sizable, depends strongly on solar zenith angle, surface albedo, altitude, and wave‐length regime. Various atmospheric photodissociation processes are categorized by spectral type based upon the wavelength regime in which the photodissociation process occurs. Three basic wavelength regimes are noted, and results characteristic of each regime are presented. Adjustment factors are provided for generalizing the pure absorption calculations.

Since 1976 the greatest concern about potential perturbations to stratospheric ozone has been in regard to the atmospheric release of chlorofluorocarbons. Consequently, atmospheric measurements of ozone have usually been compared with model calculations in which only chlorocarbon perturbations are considered. However, in order to compare theoretical calculations with recent measurements of ozone and to project expected changes to atmospheric ozone levels over the next few decades, one must consider the effect from other perturbations as well. In this paper, we consider the coupling between several possible anthropogenic atmospheric perturbations. Namely, we examine the effects of past and possible future increases of chlorocarbons, CO2, N2O, and NOx. The focus of these calculations is on the potential changes in ozone due to chlorocarbon emissions, how other anthropogenic perturbations may have influenced the actual change in ozone over the last decade, and how these perturbations may influence future changes in ozone. Although calculations including future chlorocarbon emissions alone result in significant reductions in ozone, there is very little change in total ozone over the coming decades when other anthropogenic sources are included. Increasing CO2 concentrations have the largest offsetting effect on the change in total ozone due to chlorocarbons. Owing to the necessity of considering emissions from a number of trace gases simultaneously, determining expected global‐scale chemical and climatic effects is more complex than was previously recognized.